1. Field of the Invention
The invention concerns a method and an arrangement for the controlling of the process flow in data processing installations with memory control and microprogram control which is dependent upon a central clock pulse generator whose clock pulses continuously form operating cycles for the execution of elementary operations of the microprogram control within the framework of the normal operating cycle and which can be stopped in the case of the occurrence of an event which interrupts the normal flow, such as an error, by means of a monitoring device in connection with a test device at the end of the operating cycle in progress in each case.
2. Prior Art
Due to the very complex structure of modern data processing installations, the occurrence of errors can never be excluded. In order to attain error-free results, it is necessary to make arrangements so that errors which occur can be detected and corrected. As a result, after determination of an error, the program in progress must first be interrupted.
In the German AS No. 2,248,451, an arrangement for monitoring for the presence of an error and the stopping of the generator which provides the operating clock pulses is provided. With a test clock pulse inserted at the end of the machine cycle, all monitoring points of the installation are interrogated and when an error is detected, the clock pulse generator is stopped during a time in which all data are still present in the registers for the operation which has just been carried out. The stopping of the installation with the last clock pulse in the machine cycle also has the advantage that after replacement of the erroneous data in the registers, a simple restarting is possible.
According to the German AS No. 2,324,906, in the case of the identification of an error, the installation is set back into a former state, and following this the flow of control steps bringing about the error is repeated with reduced clock pulse frequency more slowly and where applicable without error. As explained in the Germany Pat. No. 2,737,133 (column 3, line 68 through column 4, line 8), however, in the case of microprogram control units, the problem of the spreading of the effects of errors is not prevented particularly when the cause of the error extends over several elementary operations.
In the arrangement described in the German Pat. No. 2,737,133, there is coupled with the error register (which operates as monitoring device) an analysis network, which, via a pause generator, stops the clock pulse generator in each case before the clock pulse of the operating cycle introducing a new elementary operation and an error treatment routine is prepared. Then, after the passage of the pause time preset by means of the pause generator, the routine is started with release of the pulse. This known arrangement thus only reacts to errors which require a transfer into an error treatment routine.
In the case of modern installations, interruptions of the normal flow can be necessary not only due to errors of various kinds, such as hardware errors or program access errors, but also can be necessary due to further events, such as stopping or resetting of the installation, and the results of address comparisons with different reactions. It is necessary that the installation in the case of each interruption of the normal flow always assumes an unambiguous and reproducible state which permits a return into the normal operating flow without difficulty and excludes critical time conditions. Also, the parallel operation of independent functional units of the installation should thereby not be unnecessarily hindered.